Achilles (Greek 'Ἀχλύς') is the spirit of the fog of death and the personification of sorrow and misery. She is often described as a woman, or an old woman. Little is known about Achlys, except that she may have been created before Chaos, but in some myths Chaos is said to be her father and in others it is told that she cannot be equated with a lesser goddess, for she came before even the Titans.
The goddess was old even before Gaia awoke for the first time, for misery is eternal. Possibly she is the daughter of the elders, of Chaos and Night. She is the Protogenoi (Primordial God) of misery and poison and is the resident and domiciled guardian of the mist of death.
Among her abilities, the one that is common in the tales is that she can appear in people's dreams, thus being a prelude to chaos; one who dreams of Achilles will become a poor wretch.
Achilles looks like a victim of starvation, legends tell of her illustrious dripping nose, blood-red cheeks dripping blood from her huge tattered dress, tangled gray hair, and large amounts of dust covering her thin body, huge long dirty fingernails.
Presumably she has the powers of a goddess, but infinitely greater, since she is a Primordial and like the goddess of poisons, has Toxikinesis, i.e. she has absolute control and divine authority over any and all poisons and obviously control over the Death Mist.
Some myths list Achlis as a possible daughter of Nyx, but being one of the Keres, but it is not uncommon to list her as one of Hades' daughters. This mirrors how some Greek creationist myths call Chaos the state before time began and a god, while others proclaim that it was Chronos or Aclis who created Chaos or existed before it, but unfortunately it is a minor god that does not have many sources and stories for us to prove the birth of the myth.